rlp: using slices.IndexFunc

rlp/encode.go

@@ -22,6 +22,7 @@ import (
 	"io"
 	"math/big"
 	"reflect"
+	"slices"
 
 	"github.com/ethereum/go-ethereum/rlp/internal/rlpstruct"
 	"github.com/holiman/uint256"
@@ -351,7 +352,10 @@ func makeStructWriter(typ reflect.Type) (writer, error) {
 	}
 
 	var writer writer
-	firstOptionalField := firstOptionalField(fields)
+	firstOptionalField := slices.IndexFunc(fields, func(f field) bool { return f.optional })
+	if firstOptionalField == -1 {
+		firstOptionalField = len(fields)
+	}
 	if firstOptionalField == len(fields) {
 		// This is the writer function for structs without any optional fields.
 		writer = func(val reflect.Value, w *encBuffer) error {

rlp/typecache.go

@@ -159,16 +159,6 @@ func structFields(typ reflect.Type) (fields []field, err error) {
 	return fields, nil
 }
 
-// firstOptionalField returns the index of the first field with "optional" tag.
-func firstOptionalField(fields []field) int {
-	for i, f := range fields {
-		if f.optional {
-			return i
-		}
-	}
-	return len(fields)
-}
-
 type structFieldError struct {
 	typ   reflect.Type
 	field int